First off, is all follower carry weight the same? If so, do some followers suffer from a penalty due to their starting armor and the lack of ability to take it away from them? I.E. - Lydia has steel armor as her starting armor, whereas Annekke Crag-Jumper has basic clothes as her starting "armor". If it does affect their carry weight, Annekke would be the better choice for pack-mule follower since she'd have more open space to carry junk for you.